(1) Field of the Invention
The present invention relates to a novel process for the preparation of stable chemiluminescent 1,2-dioxetane compounds which can be triggered to generate light. Stable, triggerable dioxetanes prepared by the present process are preferably of the formula: ##STR1## The present invention also relates to novel sulfur-substituted alkenes (vinyl sulfides) preferably of the formula: ##STR2## and stable triggerable-sulfur-substituted 1,2-dioxetanes preferably of the formula: ##STR3## a process for their preparation and a process for their use as intermediates for producing stable triggerable 1,2-dioxetanes substituted on the dioxetane ring with alkoxy, alkenyloxy, alkynyloxy, aryloxy, aralkyloxy or acyloxy groups.
(2) Dscription of Related Art
a. Synthesis of Dioxetanes
The preparation of dioxetanes with alkoxy substituents by addition of singlet oxygen to a vinyl ether is well known in the art. Singlet oxygen is typically produced by irradiation of a photosensitizing dye in the presence of oxygen but can also be generated by thermolysis of triphenylphosphite ozonide. Other methods of preparing dioxetanes with alkoxy substituents from vinyl ethers include electron-transfer oxidation with oxygen and triarylaminium cation radical salts (R. Curci, L. Lopez, L. Troisi, S. M. K. Rashid and A. P. Schaap, Tetrahedron Lett. 28, 5319-22 (1987); L. Lopez, L. Troisi and G. Mele, Tetrahedron Lett. 32, 117-20 (1991)), oxidation by Cr(VI),or Mo(VI) oxide diperoxides (R. Curci, L. Lopez, L. Troisi, S. M. K. Rashid and A. P. Schaap, Tetrahedron Lett. 29, 3145-8 (1988)) and oxidation with triethylsilyl hydrotrioxide (G. H. Posner, K. S. Webb, W. M. Nelson, T. Kishimoto and H. H. Seliger, J. Org. Chem., 54, 3252-4 (1989)). A dioxetane was produced in low yield by reaction of a dioxene compound with oxygen which had been passed through an electric discharge, apparently producing a small amount of singlet oxygen in addition to ozone (T.-S. Fang and W.-P. Mei, Tetrahedron Lett. 28, 329-21 (1987)).
All of these methods for the preparation of alkoxy-substituted dioxetanes require the preparation of the precursor vinyl ether. No reaction involving the direct introduction of alkoxy or aryloxy groups on a pre-formed dioxetane ring has been reported to the best of applicant's knowledge. There is thus a need for a general method for the preparation of a variety of alkoxy-substituted dioxetanes from a common intermediate which does not require the preparation of each individual vinyl ether precursor.
b. Sulfur-Substituted Dioxetanes
1,2-Dioxetanes with one or more sulfur-containing substituents on the dioxetane ring are known. All known examples are unstable, with most decomposing rapidly at room temperature. (W. Adam, L. A. Arias, D. Scheutzow, Tetrahedron Lett., 23(28), 2835-6 (1982); W. Adam, L. A. Encarnacion, Chem. Ber., 115(7), 2592-605 (1982); W. Ando, K. Watanabe, T. Migita, J. Chem. Soc., Chem. Commun. (24), 961-2 (1975); G. Geller, C. S. Foote, D. B. Pechmann, Tetrahedron Lett. 673-6 (1983); R. S. Handley, A. J. Stern, A. P. Schaap, Tetrahedron Lett. 26, 3183-6 (1985)). The most stable sulfur-substituted dioxetanes, derived from 4,5-dialkyl-2,3-dihydrothiophene decompose with a half-life of a few minutes at room temperature (W. Adam, A. Griesbeck, K. Gollnick, K. Knutzen-Mies, J. Org. Chem., 53, 1492-5 (1988); K. Gollnick, K. Knutzen-Mies, J. Org. Chem., 56, 4027-31 (1991)). Two spiroadamantyl-substituted dioxetanes bearing one and two sulfur substituents, respectively, on the dioxetane ring are known. Both have been reported to rapidly and completely decompose on attempted isolation at room temperature (W. Adam, L. A. Encarnacion, Chem. Ber., 115(7), 2592-605 (1982)).
c. Synthesis of Vinyl Sulfides
Vinyl sulfides containing a carbon--carbon double bond and a sulfur substituent directly attached to one of the double bond carbon atoms can be prepared by various methods known to the skilled synthetic chemist. One of the classical methods for preparation of vinyl sulfides involves the reaction of a ketone and mercaptan with TiCl.sub.4 and an amine base (T. Mukaiyama, K. Saigo, Chem. Lett., 479-82, 1973)). Vinyl sulfides have been formed by other methods which utilize titanium reagents. Vinyl sulfones are reduced at the sulfur to vinyl sulfides with LiAlH.sub.4 --TiCl.sub.4 (E. Akgun, K. Mahmood, C. A. Mathis, J. Chem. Soc., Chem. Commun, (6), 761-2 (1994)). .alpha.-Halo-sulfoxides undergo elimination and reduction with Zn--TiCl.sub.4 to form vinyl sulfides (V. Retrakul, P. Poochaivatananon, Tetrahedron Lett., 24(5), 531-4 (1983)). In each of these methods, one or both of the C--C bonds is already formed in the starting material. None of the foregoing methods involves the direct formation of the sulfur-substituted carbon--carbon double bond from two separate carbon atoms. No method of which Applicants are aware is known for creating a vinyl sulfide by coupling two carbonyl-containing compounds, one of which is a thioester, to form a double bond with a sulfur-substituent.
d. Chemically Triggerable Dioxetanes
Chemically triggerable adamantyl-stabilized dioxetanes are disclosed in U.S. Pat. No. 4,857,652 and a paper (A. P. Schaap, T. S. Chen, R. S. Handley, R. DeSilva, and B. P. Giri, Tetrahedron Lett., 1155 (1987)). These dioxetanes exhibit thermal half-lives of years but can be triggered to produce efficient chemiluminescence on demand. Benzofuranyl dioxetanes substituted with trialkylsilyl and acetyl-protected phenolic groups which produce weak chemiluminescence have also been reported (W. Adam, R. Fell, M. H. Schulz, Tetrahedron, 49(11), 2227-38 (1993); W. Adam, M. H. Schulz, Chem. Ber., 125, 2455-61 (1992)). Each of these dioxetanes was prepared by dye-sensitized photooxygenation of a vinyl ether (alkene) precursor.
e. Enzymatically Triggerable Dioxetanes
Enzymatic triggering of adamantyl-stabilized 1,2-dioxetanes are described in U.S. Pat. No. 4,857,652 and a series of papers (A. P. Schaap, R. S. Handley, and B. P. Giri, Tetrahedron Lett., 935 (1987); A. P. Schaap, M. D. Sandison, and R. S. Handley, Tetrahedron Lett., 1159 (1987) and A. P. Schaap, Photochem. Photobiol., 47S, 50S (1988)). These dioxetanes bear a protected aryloxide substituent which is triggered to decompose with emission of light by the action of an enzyme in an alkaline aqueous buffer to give an aryloxide intermediate dioxetane which decomposes with emission of light at a greatly increased rate. Chemiluminescence is thereby emitted at a much greater intensity than that resulting from slow thermal decomposition of the protected form of the dioxetane. Further examples of enzymatically triggered dioxetanes are disclosed in U.S. Pat. No. 5,068,339 to Schaap, U.S. Pat. Nos. 5,112,960 and 5,220,005 and a PCT application (88 00695) to Bronstein U.S. Pat. No. 4,952,707 to Edwards, U.S. Pat. No. 5,132,204 to Urdea, U.S. Pat. No. 5,248,618 to Haces and PCT application WO94/10258 to Wang and in a publication (M. Ryan, J. C. Huang, O. H. Griffith, J. F. Keana, J. J. Volwerk, Anal. Biochem., 214(2), 548-56 (1993)). The enzymatically triggerable dioxetanes are now undergoing widespread use as substrates for marker enzymes in numerous applications including immunoassays, gene expression studies, Western blotting, Southern blotting, DNA sequencing and the identification of nucleic acid segments in infectious agents.
New processes for the preparation of existing and new triggerable dioxetanes are desirable to advance the state of the art. Processes which permit the preparation of dioxetane compounds which are difficult or impossible to prepare by known methods would be particularly desirable. The process of the present invention provides such means.